However, as a complicating factor, the degree of fractionation (i.e. change in isotope ratio) occurring due to photosynthesis is not entirely dependent on the water drawn up by the plant, as fractionation can occur as a result of preferential evaporation of H216O - water bearing lighter oxygen isotopes,[clarify] and other small but significant processes.
Since evaporation causes oceanic and terrestrial waters to have a different ratio of 18O to 16O, the Dole effect will reflect the relevant importances of land-based and marine photosynthesis.
[7] The stability (to within 0.5‰) of the atmospheric 18O to 16O ratio with respect to sea surface waters since the last interglacial (the last 130 000 years), as derived from ice cores, suggests that terrestrial and marine productivity have varied together during this time period.
Millennial variations of the Dole effect were found to be related to abrupt climate change events in the North Atlantic region during the last 60 kyr (1kyr=1000years).
[8] High correlations of the Dole effect to speleothem δ18O, an indicator for monsoon precipitation, suggest that it is subject to changes in low-latitude terrestrial productivity.